Various cobalt oxide spinels coated onto electrically-conductive substrates, especially for use as anodes in brine electrolysis, are known. Of particular relevancy are U.S. Pat. Nos. 3,977,958; 4,061,549; and 4,142,005; all of which are incorporated herein by reference.
Also of various degrees of relevancy are U.S. Pat. Nos. 4,073,873; 3,711,382; 3,711,397; 4,028,215; 4,040,939; 3,706,644; 3,528,857; 3,689,384; 3,773,555; 3,103,484; 3,775,284; 3,773,554; 3,632,498; and 3,663,280.
Nickel is well known as the standard anode material for commercial water electrolyzers because of its good chemical stability in the alkaline electrolyte (e.g., 25% KOH) normally employed. However, the over-voltage for O.sub.2 evolution on Ni is high and increases in service, so improved electrocatalysts are desired. Electrode coatings of mixed Ru-Ti oxides (e.g., U.S. Pat. No. 3,632,498 and others) are very good anodes for production of chlorine from NaCl brine, which is acidic; these anodes are also good for production of oxygen from acidic solutions, e.g., H.sub.2 SO.sub.4 solutions. However, their chemical stability in strongly alkaline environment, as in commercial water electrolyzers, is inadequate. Graphite is historically well known as a useful anode for Cl.sub.2 production, but is rapidly destroyed by oxygen if used for water electrolysis.
British Pat. No. 1,461,764 discloses methods of preparing anode coatings of nickel-cobalt spinel, NiCO.sub.2 O.sub.4. The use of these anodes for alkaline water electrolysis has been proposed (see, for example, pp. 63-76 and 161-168 in the Proceedings of the Symposium on Industrial Water Electrolysis, S. Srinivasan, F. J. Salzano, and A. R. Landgrebe, Eds;, Proceedings Volume 78-4 of The Electrochemical Society, Inc., Princeton, N.J.). This anode material has not met with commercial acceptance, possibly because the recommended manufacturing method involves uneconomical materials and procedures (e.g., freeze-drying, Teflon-bonding).
It has now been found that electrodes coated with cobalt-containing spinel, described hereinafter, are especially suitable and economical for the production of oxygen by the electrolysis of alkaline, neutral, or acid solutions or non-aqueous solutions of adequate conductivity.